State-dependent variation in the inhibitory effect of (D-Ala sup 2 , D-Leu sup 5 )-enkephalin on hippocampal serotonin release in ground squirrels

Journal Article · Mon Jan 01 04:00:00 EST 1990 · Life Sciences; (USA)

OSTI ID:5922677

Kramarova, L I; Lee, T F; Cui, Y; Wang, L C.H. ^[1]

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1. Univ. of Alberta, Edmonton (Canada)

Accumulated evidence has suggested that increased endogenous opioid activities may facilitate the onset of hibernation either directly or possibly through modulation of other neurotransmitter systems. The seasonal change of (D-Ala{sup 2}, D-Leu{sup 5})-enkephalin (DADLE), a {delta} receptor agonist, in modulating K{sup +}-induced ({sup 3}H)-5-hydroxytryptamine (5-HT) release from the hippocampal and hypothalamic slices of euthermic and hibernating Richardsons' ground squirrels was therefore investigated. DADLE had no effect on 5-HT release in the hypothalamic slices but elicited a dose-related inhibition on ({sup 3}H)-5-HT release from the hippocampal slices of the euthermic ground squirrel. The inhibitory effect of DADLE was completely reversed by naloxone, but not by tetrodotoxin. In contrast, DADLE failed to alter the K{sup +}-induced 5-HT release from the hippocampal slices of the hibernating ground squirrel. This state-dependent reduction in responsiveness to an opioid is consistent with the hypothesis that enhanced endogenous opioid activity in the hibernating phase could lead to down regulation of the opioid receptors and minimize its inhibition on hippocampal serotonergic activity. A high 5-HT activity would inhibit midbrain reticular activating system indirectly through non-serotonergic fibers, which in turn facilitate the onset or maintenance of hibernation.

• OSTI ID: 5922677
• Journal Information: Life Sciences; (USA), Journal Name: Life Sciences; (USA) Vol. 48:2; ISSN 0024-3205; ISSN LIFSA
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ALKALI METAL COMPOUNDS
ANIMALS
AUTONOMIC NERVOUS SYSTEM AGENTS
BIOCHEMICAL REACTION KINETICS
BODY
BRAIN
CENTRAL NERVOUS SYSTEM
DOSE-RESPONSE RELATIONSHIPS
DRUGS
ENDORPHINS
ENKEPHALINS
HIBERNATION
HIPPOCAMPUS
HYDROGEN COMPOUNDS
INHIBITION
ISOTOPE APPLICATIONS
KINETICS
MAMMALS
MEMBRANE PROTEINS
NERVOUS SYSTEM
NEUROREGULATORS
ORGANIC COMPOUNDS
ORGANS
PEPTIDES
POLYPEPTIDES
POTASSIUM COMPOUNDS
PROTEINS
REACTION KINETICS
RECEPTORS
RODENTS
SQUIRRELS
TRACER TECHNIQUES
TRITIUM COMPOUNDS
VERTEBRATES